The IMF's Christine Lagarde has issued a stark warning to the US. Photograph: Handout/Getty Images

Comparisons have been made in recent weeks between a possible US debt default and the collapse of Lehman Brothers five years ago. In one sense these parallels are valid: were the US to start welching on its creditors, the impact would be swift and profound. The winter of 2013-14 would be a re-run of the Great Recession of 2008-09.

But nobody saw Lehman's coming. The markets assumed that the US Treasury would find a buyer for the stricken investment bank because this is what had happened with Bear Stearns six months earlier and with Long Term Capital Management, the hedge fund that got into trouble in the late 1990s. Lehman's was a gigantic cock-up and a gigantic surprise.

There can be no such excuses this time. All of the key players in Washington know what is at stake and if they don't, they are unfit for office. Warnings have been raining down thick and fast – the latest coming from Christine Lagarde at the IMF and Ángel Gurría at the OECD.

The heads of these two international organisations know what they are talking about. Recovery from the Great Recession has been nothing to write home about. America's growth is anaemic by usual standards, the big emerging markets are slowing; the euro area is barely out of intensive care. It would not take much to trigger a second financial and economic crisis.

But policymakers in Washington know this. They know that a US debt default is no small matter and know what the consequences of a fresh crash will be. All of which suggests that somebody – almost certainly the Republicans – will back off before 17 October. The alternative is that, in a competitive field, the current vintage of US politicians will become infamous as the most incompetent in history.